No, it's not a plausible scenario because, if you look at the wings and power plant they are the exact same of the existing 747-400 aircraft. I'm being picky about the wings because the invented aircraft seems to be much too heavy for the lift capability it has.
Lift versus weight is an important criteria when designing a new aircraft. In this case, the lift versus weight ratio is going way down, the weight is drastically increasing but the wing area or aspect ratio isn't increasing, neither is the power generated by the engines.

You folks can always dream of it, but it will never fly.

The A380 will exist in reality, yes, because the wing area is large enough to support all the weight of this giant double decker. I don't know how much power each engine will generate but I suppose each will generate a bit more than what a 747-400 engine generates.

Discussing the lift capability of say a 747-200 or -300...
A cargo aircraft of the type is capable to carry 112 metric tons of payload.
Each passenger averages 100 KG with his baggages.
xxx
So, the weight of 1,120 passengers could be carried in a 747-"700"...
They would not be "payload" limited. They would be "bulk limited".
Where would you put that many people even with that configuration.
xxx
In Japan, they have some 747-400D with nearly 600 seats.
"Sardines" class.
So, in stretching the upper-deck all the way back, that could give room to some 700-800 people.
That is much less than the lift capability of a 747...
xxx
Happy contrails
(s) Skipper

As I remember reading somewhere, Boeing looked into the possibility of expanding the capacity of the 747 into a proposed -500,-600,-700 series, but discovered an entirely new wing technology would be needed. Considering the limited need at that time for ultra-large transports, the costs far outweighed the possible benefits.

I am curious to see how Airbus will do with the A380 - I don't see the worldwide need for that aircraft at this moment, but if they want to build it, and airports think they can handle it, be my guest. I think the future is in the longer range planes like the 772LR and A340LR.

Some of the original 747 concepts (60s vintage) were twin deck, but if you're only transporting 350 people with those day's materials, there is a weight penalty to two decks compared to one. Remember that in those days the 747 was a big single decker with a hump. Also, the twin deck proposals could not have been used for cargo like the 747. Since Boeing expected the 747 to become a cargo hauler after SSTs took over, cargo was a big priority.

Amusingly, one of the 747 proposals ("The Anteater") had a single deck like the 741, but instead of the hump it had a lowered flight deck in best Beluga style. The objective, just like with the hump, was to ease loading of cargo.

In the early 70s, after the 747-100 was well established, Boeing looked at the following:

Short-range:
1. 527 pax baseline - plain 741 with lots of seats.
2. 716 pax - 300 inch plugs fore and aft of the wing. Upper deck unchanged.
3. 666 Pax - 60 inch plug fore and 140 inch aft of the wing. Upper deck stretched to the wing.
4. 847 pax - double deck to the fin, where the fuse comes down in a way similar to the SP
5. 1000 pax - 160 inch plug fore and 140 inch plug aft of the wing, double deck to the fin, where the fuse comes down in a way similar to the SP.

The oil crisis put paid to all these fun plans, but it's interesting to note how the A380 concept could have flown back in 1980 or so.

(Source - "Boeing 747 Design and Development Since 1969" by Guy Norris and Mark Wagner).

So it is definitely possible, but unlikely now. In the 70s, the 747 wing was state of the art. Nowadays it's rather dated. And if you're going to redo the wing, you've basically rebuilt the aircraft from the ground up anyway.

EDIT: The book has some interesting concept drawings of all this stuff, and pics of the 60s double-decker and anteater models. ISBN 0-7603-0280-4.

[Edited 2004-04-07 20:07:29]

[Edited 2004-04-07 20:15:01]

[Edited 2004-04-07 20:19:20]

"There are no stupid questions, but there are a lot of inquisitive idiots."

Stalionblue, excellent analysis and I have that book, a great reference. Let me add that Boeing said when peddling its' 747X 3 1/2 years ago that it didn't make sense to the upper deck the full length of the aircraft due to the structural weight and aerodynamic penalty it would entail. Obviously, the wings would have to be completely redesigned and enlarge to support such a beast. This is a 'what-if' example that will never happen.

Alessandro, you could go with new wing, new engines, new gear. But the 747 gains much aerodynamic advantage from area ruling, and this would be lost with a complete double decker. And that's why the stretch proposals (-500x and -600x) still only had the upper deck to the wing.

"There are no stupid questions, but there are a lot of inquisitive idiots."

In studies I've read it certainly is possible and studied by Boeing as a possible growth of -300. However, as has been said before, it was not the most efficient design. The -400 is supposedly the best compromise with that basic fuselage design and size and aerodynamic economies. That was published as the -300 was being made so what changes in propulsion options that are now available might barely make it more possible but, as Boeing has said many times and is trying to prove it with the 7E7, today's market choices must be made based on lowest operating price. And it was also written before todays fuel price hikes. But yes, It would fly.